1. Field of the Invention
The present invention generally relates to the manufacture of electronic circuits and, more particularly, to a module structure and a simple process for card assembly by Direct Chip Attachment (DCA), using electrically conductive adhesives, which are reworkable.
2. Background
An involved card assembly attach process exists for Direct Chip Attachment (DCA). Unique decals are fabricated with a plated solder pattern corresponding to the chip pad footprint. These decals are accurately positioned onto the intended footprint of the chip carrier and the solder is subsequently transferred to the carrier sites in a reflow oven. The soldered pads are then leveled mechanically for coplanarity and finally the chips are placed and reflowed.
Solder alloys are used pervasively to interconnect components to carriers. Undesirable attributes of solder alloys include high temperature joining, cleaning/residues, fatigue life and the environmental ramification of lead (Pb).
Moore et al., U.S. Pat. No. 5,120,678, disclose a method for assembling an integrated circuit component to a substrate by a solder by interconnection that is reinforced by a polymer film. While this method encapsulates ball grid arrays with a thermoset adhesive, the thermoset is not reworkable.
An alternative to solder DCA is electrically conductive adhesive joining. Screen printing 0.004" features on 0.008" centers is possible with some electrically conductive adhesives.
U.S. Pat. No. 5,074,947 to Estes and 5,086,558 to Grube, disclose attaching flip chips to substrates using conductive polymer materials. All the above cited patents are incorporated herein by reference.